Primary antiphospholipid syndrome evolving into systemic lupus erythematosus: may antinucleosome antibodies be predictive?

Objective: It was reported by several groups that patients diagnosed as primary antiphospholipid syndrome (PAPS) had developed a full-blown systemic lupus erythematosus (SLE) even after many years of follow-up. Little is known about clinical and/or serological factors that may help predict such evolution. Antinucleosome antibodies (anti-NCS) were described to appear in early stages of SLE, in particular before anti-dsDNA antibodies. The aim of the study is to evaluate the prevalence of anti-NCS in a large cohort of PAPS patients. Methods: IgG and IgM anti-NCS antibodies were detected using a home made assay with H1-stripped chromatin as antigen. Sera from 106 PAPS patients were tested; 52 of them were also tested during the follow-up, at least 2 years apart form the basal sample. Results: Medium-high titre anti-NCS were found in nearly half of the patients (49/106, 46%), more frequently in those presenting features of “lupus like disease”. Most of patients displayed an unchanged pattern of anti-NCS over time. We describe three cases of PAPS patients that developed SLE after many years of follow-up; high titre and low titre anti-NCS were present in two and one of them respectively several years before evolving into SLE. Conclusions: A significant proportion of PAPS patients displayed medium-high titre anti-NCS, suggesting that the autoimmune response against chromatin may be a relevant event not only in patients with SLE. Further studies are warranted to explore the predictive value of anti-NCS with respect to the evolution from PAPS to SLE.